Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1997-08-27
2001-03-20
Sellers, Robert E. L. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C428S297400, C524S589000, C524S590000, C525S403000, C525S457000, C525S907000
Reexamination Certificate
active
06204342
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a method of chemically thickening resins.
Various resins, such as ethylenically unsaturated resins, are utilized in a wide variety of end-use applications. For example, unsaturated polyester resins are particularly desirable as molded articles including bathtubs, water tanks, and automobile parts. In these instances, reinforcing fibers are typically blended with the resins to impart strength and lightweight dimensional stability to the article. Sheet molding compound (“SMC”), for example, is a mixture or combination which includes one or more resins, along with reinforcing fibers and inert fillers.
In particular, the automobile industry is increasingly using molded articles made from reinforced resins in place of heavier metal articles in order to provide more fuel efficient automobiles. Strength requirements in such applications are significant, and accordingly fibrous filaments are employed in high amounts, typically above 50 percent based on the weight of the article. Resin compositions containing such a high fiber amount, however, are often difficult to mold into articles with the reinforcing materials uniformly distributed.
More specifically, the production of molded articles with intricate shapes involves squeezing the reinforced resin material between male and female sections of a mold. Often during this process, a sizeable quantity of resin is forced out of the mold, typically exceeding 30 percent of the total weight. As a result of the sizeable resin loss, the formed article often becomes more highly filled in the region of the preform and is sparingly filled at the mold extremities or locations of maximum flowout.
To help enhance the physical properties of such formed articles, thickening materials have thus been employed. Conventional thickening materials have been in the form of metal oxides. Resins using the metal oxides, however, have been observed to display undesirable physical properties relating to brittleness and reduced moisture resistance.
As an alternative, isocyanate-containing resins have been proposed as chemical thickeners, such as described, for example, in U.S. Pat. No. 4,232,133. The ‘133 patent discloses the use of gels of ethylenically unsaturated monomer solutions which contain isocyanate resins. The resins are disclosed to be useful as SMC. The isocyanate resins are potentially advantageous relative to the metal oxides in that they exhibit improved stability and can be matured to form moldable compositions within a few hours.
Difficulties exist in using isocyanates as thickening resins. In particular, isocyanates in general are highly moisture sensitive. In such instances, side reactions often take place which produce urea and carbon dioxide. As a result, thickening tends to be non- uniform, thus adversely affecting thermal and hydrolytic stability of the resin, and resin physical properties.
In view of the above, there remains a need in the art for a method which allows for a resin to be chemically thickened while minimizing adverse effects to physical properties of the resulting article formed from the thickened resin.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method for chemically thickening a resin which minimizes adverse physical effects to the thickened resin.
It is a further object of the invention to provide a cured resin from the chemically thickened resin.
To this end and others, the present invention provides a method of thickening a resin. The method comprises blending (1) a resin containing active hydrogens; and (2) a polycarbodiimide, and (3) an organic diluent to form a reactive mixture, and then reacting the resin containing active hydrogens and the polycarbodiimide to chemically bind the resin and polycarbodiimide. Resins which contain active hydrogens are preferably saturated polyester resins, unsaturated polyester resins, vinyl ester resins, polyurethane resins, and mixtures thereof.
The chemically bound resin may further be cured to form a crosslinked resin material. In one embodiment, the curing step may be carried out in the presence of an initiator. In addition to the initiator, the curing step may be carried out in the presence of a promoter.
The polycarbodiimide of the present invention is preferably formed from a reaction between an isocyanate-containing intermediate and a diisocyante. The isocyanate-containing intermediate is preferably formed from a reaction between a component containing active hydrogens and a diisocyanate. In another embodiment, the polycarbodiimide may be formed from the polymerization of diisocyanates and the subsequent reaction with a component containing active hydrogens to form the polycarbodiimide.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention will now be described more fully hereinafter, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
The present invention relates to a method of thickening a resin containing active hydrogens. The method includes blending a resin containing active hydrogens, a polycarbodiimide, and an organic diluent to form a reactive mixture. The polycarbodiimide is preferably present in the organic diluent when added to the resin containing active hydrogens during this step. The reactive mixture preferably contains greater than about 5 percent by weight of polycarbodiimides.
Subsequently, the resin containing active hydrogens and the polycarbodiimide are reacted to chemically bind the resin containing active hydrogens and the polycarbodiimide, in other words, chemically thicken the resin containing active hydrogens. This step may be carried out at a temperature between about 5° C. and about 60° C. The chemically thickened resin preferably has a viscosity ranging from about 30,000 centipoise to about 50 million centipoise, and more preferably from about 100,000 centipoise to about 20 million centipoise.
Additionally, the chemically bound resin may be cured to form a cured (i.e., crosslinked) resin material. The curing is preferably carried out at a temperature ranging from about 40° C. to about 150° C., and more preferably from about 50° C. to about 100° C. The invention is advantageous in that the glass transition temperature (T
g
) of cured resin material is enhanced by virtue of the method disclosed herein. Preferably, the T
g
of the cured resin material increases from about 5 percent to about 600 percent upon undergoing thickening and curing, and more preferably from about 10 percent to about 300 percent.
As a result of this elevation in T
g
, it is believed that the physical properties of the cured resin material subsequent to thickening and curing are enhanced. Preferably, the cured resin material has a flexural strength ranging from about 3000 psi to about 80,000 psi; a tensile strength ranging from about 1000 psi to about 50,000 psi; and a percent elongation ranging from about 1 to about 1000. In addition to the above, it should be appreciated that various types of resins may have differing preferred ranges of physical property values. For example, cured unsaturated polyester resins preferably have tensile strengths ranging from about 3000 psi to about 50,000 psi and elongations ranging from about 1 to about 10 percent, while cured hot melt adhesives preferably have tensile strengths ranging from about 800 to about 5000 psi and elongations ranging from about 70 to about 1000.
Preferably, the reactive mixture contains between about 3 to about 50 percent by weight of polycarbodiimide, more preferably between about 3 and about 20 weight percent polycarbodiimide, and most preferably between about 6 and about 12 weight percent polycarbodiimide.
The invention also relates to a method of forming a reinforced product.
Myers Bigel Sibley & Sajovec P.A.
Reichhold Chemicals
Sellers Robert E. L.
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